Brief Summary Of The Invention
Interest in the use of coal rather than oil is intense due to the size of the reserves of coal in comparison with the size of the reserves of oil and also the desire of countries with reserves of coal but small reserves of oil to lessen or even free themselves of dependence for energy upon countries which produce and export oil.
A market where coal presents no competition for oil is for mobile motor fuel. All the world's cars, trucks and trains run on gasoline or diesel fuel, with the very minor exception of a few electric vehicles confined to short runs around the most intensely urbanized areas. The dominance of oil in the mobile motor fuel market is due to the oil refinery. Without an oil refinery, the ash, sulfur and tar present in crude oil would preclude its use in internal combustion engines.
The natural fuel product from coal, free of ash, sulfur and tar, is carbon. Up to the making of the present invention, no sensible way existed to produce essentially pure carbon from coal. The coking of coal leaves all of the ash and a great deal of the sulfur in the coke, and therefore is not a way of producing essentially pure carbon from coal.
The present invention, on the other hand, provides a method for producing finely divided carbon from coal by reacting coal and air in a slagging ash gasifier to produce a gaseous mixture containing carbon monoxide, separating the carbon monoxide from the gaseous stream, and disproportionating the carbon mixture to produce finely divided carbon and carbon dioxide. At least a portion of the carbon dioxide produced by the disporportionation is returned to the gasifier.
The finely divided carbon is a suitable fuel for use in an internal combustion engine, for example, a diesel engine. When used as a fuel in an internal combustion engine, the exhaust from the engine contains essentially no pollutants, such as compounds containing carbon and hydrogen, compounds containing sulfur, or compounds containing lead. No catalytic converter, which increases considerably the cost of a vehicle powered by a fuel containing carbon and hydrogen, is needed.
The finely divided carbon, being essentially free from sulfur, can also be used advantageously as a fuel in the heating of buildings or for the generation of steam or electricity in centers of high density population.
Processes are known for the conversion of coal into liquid fuel suitable for use in an internal combustion engine, perhaps the most efficient of which is the Fischer-Tropsch process practiced in the South African Sasol Plant, mentioned on page 672 of Volume 5 of Kirk-Othmer, Encyclopedia of Chemical Technology (Second Edition, 1964).
When this invention is practiced, in a preferred embodiment, the product is carbon dust. The energy recovery from coal is much greater than is the case when liquid fuel is produced by the Fischer-Tropsch process. In addition, only one-fifth to one-tenth as much work [compressors, etc.] is needed to produce carbon as to produce liquid hydrocarbons from coal.